In a recent railroad system, an electric railway vehicle (hereinafter referred to simply as electric vehicle) having a regenerative brake is popular. However, if there are only a small number of, or no, other electric vehicles operating as a load that consumes regenerative power fed back to an alternating current (AC) distribution line from the electric vehicles, excess regenerative power is returned to the electric power company via an electric power substation (hereinafter referred to simply as substation), thereby preventing effective utilization of the regenerative power. In addition, a direct current (DC) distribution line may result in regeneration cancellation, thereby possibly preventing use of a regenerative brake.
To address the problem described above, Patent Literature 1 discloses a system that charges an electrical power storage apparatus using regenerative power when there are no electric vehicles that consume the regenerative power. When the distribution line voltage, equal to the feeder voltage, reaches or exceeds a charge start voltage, this system converts the regenerative power into DC power to charge the electrical power storage apparatus, while when the distribution line voltage reaches or fall below the discharge start voltage, this system discharges electrical power stored in the electrical power storage apparatus to the distribution line. In this relation, if the charge start voltage is fixed, when the distribution line voltage increases and reaches the charge start voltage during no-load hours, such as in an early morning or late at night, the electrical power storage apparatus may be charged with electrical power supplied from a substation, rather than with regenerative power from an electric vehicle, thus causing cross current. To avoid occurrence of cross current, the system of Patent Literature 1 monitors the distribution line voltage for a certain time period to calculate an average voltage, and sets the charge start voltage to a voltage value that is several volts higher than the average voltage of the distribution line voltage.
In addition, to address the problem described above, Patent Literature 2 discloses a system that utilizes a phenomenon that an output voltage of a rectifier installed in a substation has a ripple component, which is a frequency component, while, in contrast, a regenerative voltage of an electric vehicle has no ripple components, to estimate the no-load voltage on the basis of a determination that a distribution line voltage without ripple components is identical to the ripple peak voltage, and thus periodically resets the regeneration start voltage on the basis of the estimated no-load voltage.